The Cancer Surveillance Program (CSP) is a rapid ascertainment population based tumor registry for Los Angeles County. All case-control studies described in the Program Project Grant application, as well as a series of separately funded analytic epidemiologic studies with total annual budgets exceeding 4 million dollars, depend on the CSP for case identification. Funds requested by this application will support the rapid ascertainment component of the CSP. After July 1, 1987, we expect the other major CSP activities (abstracting, processing, and analysis of the medical record data items which are essential to descriptive epidemiology) to be funded by the State of California. The major focus of the CSP has always been and will continue to be etiologic research. The major distinctive features of the CSP include (1) the size and diversity of the population base; (2) active as opposed to passive surveillance; (3) optimum cost-effectiveness; and (4) rapidity of case ascertainment. The latter feature is the highest priority of the CSP. Through new techniques initiated in the last year, including immediate entry of a minimal data set on each new histologically diagnosed cancer case using lap-top microcomputers available to all Field Technicians for data entry case ascertainment is now over 50% complete within one month of diagnosis and essentially 100% complete within 2 months. The active population-based rapid ascertainment feature contributes greatly to the quality of case-control studies done by this program.